1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member and to a process cartridge and an electrophotographic apparatus each including the electrophotographic photosensitive member.
2. Description of the Related Art
Nowadays, electrophotographic photosensitive members containing organic photoconductive substances predominate are the mainstream of electrophotographic photosensitive members for use in process cartridges and electrophotographic apparatuses. In general, an electrophotographic photosensitive member includes a support and a photosensitive layer formed on the support. To inhibit the charge injection from the support side to the photosensitive layer side and inhibit the occurrence of image defects, such as fog, an undercoat layer is provided between the support and the photosensitive layer.
In recent years, charge-generating substances having higher sensitivities have been used. However, there is a problem in which a higher sensitivity of a charge-generating substance result in a larger amount of charges generated; hence, the charges are liable to stay in the photosensitive layer, thereby easily causing a ghost. Specifically, a phenomenon, i.e., a positive ghost phenomenon, in which the density is increased at only a portion of an output image corresponding to a portion that has been irradiated with light at the time of previous rotation, is liable to occur.
As a technique for inhibiting (reducing) such a ghost phenomenon, a technique for incorporating an electron-transporting substance into an undercoat layer is known. In the case where the electron-transporting substance is incorporated into the undercoat layer in order not to elute the electron-transporting substance at the time of the formation of the photosensitive layer on the undercoat layer, a technique for using an undercoat layer composed of a curable material that is not easily dissolved in a solvent of a photosensitive layer coating liquid is known.
PCT Japanese Translation Patent Publication No. 2009-505156 discloses an undercoat layer which contains a condensation polymer (electron-transporting substance) having an aromatic tetracarbonylbisimide skeleton and a cross-linking site and which contains a polymer with a cross-linking agent. Japanese Patent Laid-Open Nos. 2003-330209 and 2008-299344 disclose an undercoat layer containing a polymer of a non-hydrolyzable polymerizable functional group electron-transporting substance.
In recent years, electrophotographic images have been required to have better image quality, so the tolerance for the foregoing positive ghost has been extremely tightened.
The inventors have conducted studies and found that with respect to the inhibition (reduction) of the positive ghost, in particular, a change in the level of the positive ghost before and after continuous image output, the techniques disclosed in PCT Japanese Translation Patent Publication No. 2009-505156 and Japanese Patent Laid-Open Nos. 2003-330209 and 2008-299344 still have room for improvement. In the techniques disclosed in PCT Japanese Translation Patent Publication No. 2009-505156 and Japanese Patent Laid-Open Nos. 2003-330209 and 2008-299344, the positive ghost is not sufficiently reduced during the initial stage and repeated use, in some cases.